Setup:

The AIX system currently has the following setup:

en1: 10.0.0.5
subnet mask: 255.0.0.0
default gateway: 10.0.0.1

Question:

How to create a VLAN adapter using base_adapter ent2 with vlan_tag_id 2030, and configure IP address 13.0.0.45 without making changes to the existing en1 configuration with default route?

Answer:

--> Step 1:

smitty vlan -> Add A VLAN -> Select ent2 -> Enter 2030 as VLAN Tag ID

This action creates a new VLAN device ent3.

--> Step 2:

smitty tcpip -> Further Configuration -> Network Interfaces -> Network Interface Selection ->
Change / Show Characteristics of a Network Interface -> Pick en3 from the list -> Fill in the fields as below.

Note: Do not select "smitty tcpip -> Minimum Configuration & Startup" option to configure en3.

As shown in the following netstat -in and netstat -rn outputs, en3 with IP address 13.0.0.45 is configured without changing en1 and default route via en1.

Conclusion:

If a system has an interface already configured with a default route, and an additional interface needs to be configured, use "smitty tcpip -> Further Configuration" instead of  "smitty tcpip -> Minimum Configuration & Startup".